从选择器中添加值，返回NAN而不是数字

Question

我总能得到南的回报。我试图让它在下面的代码中添加所有可用的选择器。看整条线。

Form = connect(state => {
  const equipmentTotal = selector(state, 'equipment.total'); 
  const softwareTotal = selector(state, 'softwares.total');
  const thirdPartyEquipmentTotal = selector(state, 'thirdPartys.totalFees');
  const miscTotal = selector(state, 'miscTotal');
  const tradeInTotal = selector(state, 'orderHeader.tradein');

  return { //Returning data like the following is the equivalent of using ({ }) which is an object-literal as an expression in ES6... docs for more info.
    total: equipmentTotal + softwareTotal + thirdPartyEquipmentTotal + miscTotal + tradeInTotal,
  };
  },
)(Form);

但是，如果单个选择器未定义(null)，则返回NAN。如果没有在状态中定义数字，是否可以将选择器设置为返回零？理想情况下，我不希望在表单字段中设置默认值0，因为它需要用户突出显示和删除它，或者可能意外地将0添加到输入数字的末尾。因此，用户在选择字段yeilding 290后不小心键入29。

Answer 1

最简单的方法是使用||(或) JavaScript运算符。它返回第一个真实值。因此，如果从选择器返回的值是undefinded、null，甚至是0，它将返回0；

Form = connect(state => {
    const equipmentTotal = selector(state, 'equipment.total') || 0;
    const softwareTotal = selector(state, 'softwares.total') || 0;
    const thirdPartyEquipmentTotal = selector(state, 'thirdPartys.totalFees') || 0;
    const miscTotal = selector(state, 'miscTotal') || 0;
    const tradeInTotal = selector(state, 'orderHeader.tradein') || 0;

    return { //Returning data like the following is the equivalent of using ({ }) which is an object-literal as an expression in ES6... docs for more info.
        total: equipmentTotal + softwareTotal + thirdPartyEquipmentTotal + miscTotal + tradeInTotal,
    };
},
)(Form);